Treatment of metal melts



Aug 23, 1966 F. HARDERs TREATMENT OF METAL MELTS 2 Sheets-Sheet 1 Filed Nov. 15, 1965 ecco Aug. 23, 1966 F. HARDERS TREATMENT OF METAL MELTS 2 Sheets-Sheet 2 Filed NOV. l5, 1965 United States Patent O 3,268,326 TREATMENT QF METAL MELTS Fritz Harders, Burenbruch, Germany, assignor to Dortmund-Horder Huttenunion Aktiengesellschaft, Dortmund, Germany Filed Nov. 15, 1963, Ser. No. 323,936 Claims priority, application Germany, Nov. 29, 1962, D 40,384 2 Claims. (Cl. 75-58) In the treatment of metal baths with solid substances, solid or liquid reaction products are frequently produced, and these must be eliminated as completely as possible from the bath. Particularly when liquid steel is being deoxidised, it is necessary, in order to obtain a high degree of purity, that the deoxidation products should rise in the melt and be eliminated from it.

It is known to degas steel baths by the application of a vacuum and for this purpose parts of the melt, held for example in a ladle, are introduced one after another through a pipe immersed in the melt into a vacuum chamber, and each part is returned to the ladle through the same pipe after the degassing. In order to achieve thorough degassing in a short time, it is necessary for the vacuum chamber to accommodate sufficiently large parts of the melt each time and each part must have a large surface area to which the vacuum is applied. Owing to the high vacuum in the chamber, the liquid metal tends to splash and froth when the gases contained in it are liberated. All these conditions make a vacuum chamber of large diameter and substantial height, with vacuum pumps of extremely high suction capacity necessary. An apparatus of the type referred to for degassing steel is therefore preferably made of. stationary construction. The introduction of the parts of the melt into the vacuum chamber is conveniently effected by hydraulic raising and lowering of the ladle containing the steel melt.

An apparatus consisting of an evacuable vessel with a pipe leading into its bottom can also be used in a conventional manner in order to generate vigorous movements in a metal bathfor example, in the melt in a Siemans-Martin furnace-in order to achieve rapid progress of the reaction between the metal bath and the slag, and rapid dissolution and uniform distribution of treatment substances added to the bath.

According to this invention, a metal bath is treated with a treatment medium by a method in which the open end of a pipe leading from the bottom of a vessel is introduced into the Ibath, the pressure in the vessel is adjusted to cause a part of the metal in the bath to ow into the vessel, the medium is introduced into the metal in the vessel to form a key alloy containing the medium and the pressure in the vessel is then raised to return the key alloy to the bath.

This method is therefore based upon the fact that, by pressure variations, an adequate portion of the melt to be treated is introduced by the liquid displacement apparatus into the vessel, a homogeneous key alloy is manufactured therefrom, and the key alloy which flows back out of the chamber into the melt to be treated is possessed of such kinetic energy that an optimum mixing of the key alloy and the melt is produced. It is impossible fo-r detectable reactions to occur between the substances and the slag covering the bath, since the pipe section of the liquid displacement apparatus leads through the slag cover directly into the metal to be treated. The combustion losses lare consequently also extraordinarily low.

The treatment substances are conveniently introduced into the vessel during the actual inflow of the liquid metal. In the case of large added quantities, it is recommended 3,268,326 Patented August 23, 1956 ICC that the liquid displacement apparatus be actuated a number of times-i.e., to proceed with la number of batches of key alloy.

The method according to the invention is also particularly suited for introducing into the metal bath, in metallurgically appropriate succession, materials which diier in their composition and in the purpose for which they are intended. For example, in the c-ase of steels to be deoxidised with 'aluminium and with silicon, it is desirable to manufacture the individual key alloys with aluminium alone at rst, and subsequently with silicon, for the sake of the better elimination of aluminium oxides. No heating of the liquid displacement apparatus is necessary during the deoxidation or alloying treatment. It is however desirable to pre-heat the vessel before using it for example, by means of gas burners.

As compared with steel degassing installations, the liquid displacement apparatus possesses a small weight and small dimensions. It can therefore be transported conveniently with the existing transport means in steelworks practice-for example, cranes--and be brought for use to the required point at any time.

Instead of deoxidation and/ or alloy media, other metaltreating substances may also be introduced into the vessel of the liquid displacement apparatus when charged with a part of the metal bath. For example, the desulphuration of a pig-iron bath is successfully accomplished if a suspension of tine-grain lime in pig-iron is manufactured in the vessel and introduced into the pig-iron bath.

Two examples of the invention will now be described with reference to the accompanying diagrammatic drawings in which:

FIGURE l is a Vertical section of a liquid displacement apparatus which operates under vacuum; and

FIGURE 2 is a section of a liquid displacement apparatus which operates under positive pressure.

As shown in FIGURE 1, a refractory-lined ladle l contains an iron melt 2 to be deoxidised. This is covered by slag 3. Into the melt 2 there plunges a refractoryclad pipe 4 which leads into the bottom of a substantially cylindrical refractory-lined vessel 5. Above the top 6 of the Vessel, there is a charging device 7 which is attached in a vacuum-tight manner and its contents can be introduced into the interior of the vessel 5 after opening a closure 8. The charging device may be subdivided into .a number of compartments to accommodate a number of deoxidation media or like treatment materials or treating agents.

A key alloy is now manufactured by plunging the pipe 4 of the cylindrical vessel 5, which conveniently has its ends sealed by a fusible slag repellent, not shown, into the bath 2 and a vacuum of approximately 1/2 atm., is then generated in the vessel 5 by means of a pump installation, not shown, via a conduit 9. A small part 10 of the metal bath then flows into the vessel 5. Simultaneously with the inowing metal, some deoxidation medium is introduced from the charging device 7 into the interior of the vessel. Normal pressure is then established in the vessel 5 via the cond-uit 9, the key alloy being thus returned into the ladle 1 and completely mixed with the iron bath. This process may be repeated a plurality of times.

With a pressure of approximately 0.4 atm. in the vessel 5, the difference in height between the bath level of the iron bath 2 and of a part 10 in the Vessel 5 .amounts to 0.85 metre. If the pipe section 4, having an inside diameter -of 0.15 metre, is plunged into the iron bath sufciently for the top edge of the base of the vessel to be located 0.25 metre above the top level of the iron bath, then the part 10 in the Vessel 5 if this has an internal height of 1 metre and an inside diameter of 0.6 metre occupies a vcharge height of 0.6 metre and possesses a weight of approximately 1.2 tons. The relatively low vacuum of 0.4 atm. prevents splashing or rothing of the melt When introduced into the vessel 5, which owing to its small weight can be operated and transported suspended Ifrom a crane.

In the case of a steel bath having a weight of 100 tons which is to be deoxidised with 100 kg. in all of aluminium, the liquid displacement apparatus is conveniently 'actuated four times, and 25 kg. of aluminium is added each time to the part of the melt present in the vessel 5.

With the liquid displacement apparatus shown in FIG- URE 2, which operates at a positive pressure, the vessel 5 is equipped with a short pipe 4. The vessel is plunged sufficiently deeply into the metal bath 2 for the part 10 of the bath which is requisite for manufacturing the key alloy to dow into the vessel, with addition of the deoxid-ationy substances in the charging device 7. By the introduction of a gas at a positive pressure of approximately 1A. at-m. through the conduit 11, the key alloy is returned into the metal bath and is mixed with it. Normal pressure is then established in the interior of the vessel 5 via the conduit 12, and :a key alloy is again produced. This cycle is repeated a sucient number of Itimes until all the deoxidation substances have been added to the iron bath. At the end of the treatment, normal pressure is adjusted in the interior of the vessel 5, and the liquid displacement Iapparatus is raised out of the metal bath,

I claim:

1. Method of treating a metal melt with treating agents -for purifying and alloying with the metal of the melt, which comprises conveying a portable receptacle to a position a'bove a rnelt, lowering an open end of the receptacle into the melt, simultaneously discharging from the receptacle part of the air therein and replacing it with a portion of the melt introduced through the open end of the receptacle, feeding a quantity of treating agent to the portion of the melt in the receptacle so that the treating agent forms an alloy with the metal melt portion, and pressurizing the receptacle to discharge the alloy formed therein into the surrounding melt.

2. Method of treating a metal melt with treating agents for purifying and alloying with the metal of the melt, which comprises conveying a portable receptacle to a position above a melt, lowering an open end of the receptacle into the melt to a specific level so that a portion of the melt entering the receptacle through the open end thereof displaces part of the air in the receptacle and discharges it through an opening -at the upper end of the receptacle, feeding a quantity of treating agent to the portion of the lmelt in the receptacle so that the treating agent forms an alloy with the metal melt portion, and pressurizing the receptacle to discharge the alloy formed therein into the surrounding melt.

References Cited by the Examiner UNITED STATES PATENTS DAVID L. RECK, Primary Examiner.

WINSTON A. DOUGLAS, Examiner.

W. C. TOWNSEND, H. W. TARRING,

Assistant Examiners. 

1. METHOD OF TREATING A METAL MELT WITH TREATING AGENTS FOR PURIFYING AND ALLOYING WITH THE METAL OF THE MELT, WHICH COMPRISES CONVEYING A PORTABLE RECEPTACLE TO A POSITION ABOVE A MELT, LOWERING AN OPEN END OF THE RECEPTABLE INTO THE MELT, SIMULTANEOUSLY DISCHARGING FROM THE RECEPTACLE PART OF THE AIR THEREIN AND REPLACING IT WITH A PORTION OF THE MELT INTRODUCED THROUGH THE OPEN END OF THE RECEPTACLE, FEEDING A QUANTITY OF TREATING AGENT TO THE PORTION OF THE MELT IN THE RECEPTACLE SO THAT THE TREATING AGENT FORMS AN ALLOY WITH THE METAL MELT PORTION, AND PRESSURIZING THE RECEPTACLE TO DISCHARGE THE ALLOY FORMED THEREIN INTO THE SURROUNDING MELT. 